Description of the Related Art
This invention relates to the field of the machines for bending pipes or section bars.
Machines for bending pipes and section bars are mainly of two types: i) bending machines or roller benders having a variable bending radius, which are able to give a pipe or a section bar a spatial torsional deformation, i.e. a helicoidal pitch, in addition to a curvature in one plane; ii) pipe benders having a fixed bending radius, which are adapted to give a pipe or a section bar only a bending in one plane.
The possibility of changing a bending radius is critical for bending machines or roller benders, as it enables to have variable distances between the axes of the bender rollers.
In this connexion a symmetrical swinging system, an asymmetrical rectilinear system and a pyramidal system are known in the field of the bending machines.
The symmetrical swinging system is shown by way of example in FIG. 1 of the accompanying drawings. There is a work table 1 on which three grooved-pulley bender rollers 2, 3, and 4 are arranged in an isosceles triangle configuration. The two rollers 3 and 4, which are located in a base of the isosceles triangle configuration, can swing in slots 3' and 4', respectively, being driven by hydraulic cylinders 3" and 4". Two pressure rolls 5, 6 in the shape of elongated cylinders, which are able to give a pipe a helicoidal pitch, are mounted near two oblique sides around pivots 5' and 6' respectively at an end approaching a vertex of the isosceles triangle configuration opposite to said base so that the pressure rolls 5, 6 can be positioned angularly.
Three bender rollers are provided also in the asymmetrical rectilinear system, with two of them being on one side defining a work area and the third one being approachable/removable along a rectilinear guide to/from this work area.
In the pyramidal system two lower bender rollers are fixed and a third bender roller can be positioned rectilinearly above the two fixed bender rollers.
The same Applicant discloses how to achieve variable distances between the axes of bender rollers in his Italian Patent Application No. RM95A000309 filed on May 12, 1995, which is entitled "Universal Bending Machine". He claims a bending machine comprising a motor and reduction gear unit; a machine box, whose work table provides two or more pairs of hollow rotary drives having fixed parallel axes of rotation, which are designed to receive firmly in their cavity in a interchangeable way rotating roller spindles driven by the motor and reduction gear unit through gears arranged in the machine box, and a slider which is movable along a guide provided through the machine box on the same surface of the rotary drives, said slider passing through the fixed distance between the axes of said pairs of hollow rotary drives and supporting one or more roller spindles.
Advantageously such a bending machine is very stiff and allows that the distance between the axes can be changed very widely; further it is more simple and ergonomic, particularly as it is two-faced, than the abovesaid conventional machines.